6-Gingerol induces cell cycle arrest. (A) Flow cytometry analysis using PI staining showing cell cycle distribution in MDA-MB-231 and MCF-7 cells after 48 h treatment with 6-gingerol. (B) Graphical representation of cell cycle distribution showing G0/G1 arrest by 6-gingerol in breast cancer cells. (C) RT-qPCR showing expression of cell cycle checkpoint genes. The representative expressions of CCND1, CCNE1, CDK4, CDKN1A, and CDKN1B mRNA are shown; Cp values were normalized to GAPDH mRNA. Controls are set to 100. ** p < 0.01 and *** p < 0.001 (ANOVA test), & p < 0.01 vs. control, and # p < 0.001 vs. control. (D) Western blotting of MDA-MB-231 and MCF-7 cells after 48 h treatment with 100 and 200 µM of 6-gingerol showing the expression of cyclin D1, cyclin E, CDK4, p21, and p27. (E) Representative protein expression was determined by densitometry and normalized to GAPDH. Controls are set to 100. Data were confirmed after repeating the experiment three times. *** p < 0.001 (ANOVA test). # p < 0.001 vs. control.